Tunnel lining



May14,1946. A. BULL 2,400,071

TUNNEL LINING Filed March 21, 1945 Fig.6

Patented May 14, 1946 UNITED STATES PATENT OFFICE f f .2,400,071 I v TUNNEL LINING Anders Bull, Forest mu IN. Y. Application March 21, 1945, Serial No. 583,946

(Clam- 15) .5 Claims.

My invention relates to the linings of tunnels in soil, such as are used for accommodating railway trains or vehicles. It is also of value for tunnels used as aqueducts and culverts of relatively large cross-section. The lining is that part of a tunnel which serves to keep the adjacent soil permanently in place.

Tunnels are constructed in soil either by the tunneling method, or by the open cut method. The tunneling method may be further subdivided into the timbering method and the shield method. In the timbering method, timbers are used as a temporary means for preventing the adjacent soil from caving in while the lining is being constructed in the bore; in the shield method, the shield, which i pushed forward as the excavation progresses, performs that function. In the open cut method, a trench is first dug, the lining is constructed in the trench and the trench is backfllled. In culvert construction it often happens that no trench is required, the lining being constructed on the ground, whereupon an embankment'is placed over it.

The lining forming this invention is preferably of a substantially circular or elliptical cross-section. Linings of that type maybe either continuous, as with a poured concrete lining, or segmental. A segmental lining is usually constructed of a series of rings placed end to end, each of which is built'up of a number of segments made of iron, steel or concrete. My invention relates substantially to tunnel linings of the segmental type.

In considering the forces to which tunnel linings in soil are subjected, it is customary to distinguish between active and passive forces. The active forces are those due to the weight of the overlying soil, the weight of the lining itself and the hydrostatic action of any water present. These forces are easily computed. The passive forces, on the other hand, are the reactions exerted by the abutting soil as the latter is being compressed. The compression is caused, in part, by the difference between those vertical force components striving to press the lining down and those tending to float it, and, in part, by the elastic deformation of the lining under the influence of all the forces acting on it.

As a rule, the downward force components predominate, causing the soil on the underside of the lining to be compressed, the resulting soil reactions being directed vertically upward. At the same time the elastic deformation ofthe lining causes some portions of it to move away from the center of the tunnel, thereby compressing the soil radially and giving rise to soil reactions which are directed toward the center.

The economic proportioning of a lining dependson a correct stress analysis which is possible only when the magnitude and distribution of the soil reactions thus produced are known. Because of their highly indeterminate character, however, they have long defied accurate analysis. Recourse has, therefore, been had to a drastic simplification of the actual conditions. The vertical'soil reactions were thus assumed to be uniformly distributed over the horizontal projection of the lining and, furthermore, only the horizontal components of the soil reactions due to the elastic deformation of the lining were considered.

If the stresses developed in the lining by bending moments and circumferential thrust are determined on this basis it is found that the stresses due to thrust are substantially the same at any point of the periphery, whereas those due to bending vary continually, reaching their highest value at the top of the lining, while secondary maxima, only slightly less in value, occur at the sides and bottom. Since the lining must be strong enough to resist the combined stresse at all of these points the accepted practice has hitherto been to make the lining of uniform strength throughout, as determined by the thrust and moment at the top.

In sharp contrast to the above are the results obtained when the soil reactions are determined by a rational method which has been developed by me, and which dispenses with the simplifying assumptions noted above. The method is explained in a paper published in the Proceedings of the American Society of Civil Engineers for November, 1944, under the title Stresse in the linings of shield driven tunnels. It is shown in the paper that when the lining is properly constructed in accordance with my theory, moments of any consequence are developed in the upper portion of the lining only, while the moments developed in the lower portion are very small, in fact small enough to be safely neglected in deter mining the strength to be provided. Said lower portion need only have sufiicient strength to resist the stress due to thrust.

Therefore, my tunnel lining is constructed with a lower portion of materially less strength than its upper portion. This is an economic departure from prior art tunnel linings in soil, such as are used, for example, in under river tunnels for railways and vehicles, where the lining is of uniform strength throughout its perimeter.

In the drawing:

Fig. 1 is a moment diagram of a properly constructed tunnel lining in soil.

Fig. 2 is a cross-section of a segmental tunnel lining, especially suitable for shield driven tunnels.

Fig. 3 is a longitudinal elevation of the lining of Fi 2.

Fig. 4 is a cross-section of a welded segmental tunnel lining, especially suitable for culverts.

Fig. 5 is a longitudinal elevation of the lining of Fig. 4.

Fig. 6 is a section taken along the line 66 of Fig. 2 and extending axially for one ring of the tunnel lining, and

Fig. 7 is a section taken along line 1-1 of Fig. 2, also extending axially for one ring of the tunnel lining.

In Fig. 1, the radial intercept, such as the one marked 8, between the circle 9 and moment graph represents the relative intensity of moment at any point of the lining. As can be seen, there is substantially no moment produced in the lower portion of the lining, extending over somewhat more than one-half the perimeter. Graph H] was determined in accordance with a correct evaluation of the soil reactions.

The segmental tunnel lining shown in Figs. 2, 3, 6 and '7 is constructed of upper segments l l and lower segments [2. Linings of this type are most- 1y circular, with the segments made of cast iron or steel held together by steel bolts l3 and H5. The segments are provided with axial flanges l8 as well as with circumferential flanges l4. Bolts l extend through the axial flanges and serve to hold together the segments of a ring, such as ring 29, Fig. 3, whereas bolts l3 extend through the circumferential flanges and serve to fasten the rings to one another. Ribs are often provided for imparting additional strength to the segments. The shell l6 and the flanges of the upper segments H are of materially greater thickness than the shell I! and flanges of the lower segments l2.

The lining shown in Figs. 4 and 5 is useful for culverts, especially those that are constructed on the ground, after which an embankment is placed over them. The material used for the segments is usually corrugated steel plate. The segments overlap one another both circumferentially, as at 26, and axially, as is shown in Fig. 5, the solid lines 2| and 23 indicating the ends of ring 19, and the dashed lines 22 and 25 the ends of rings 20 and 24, respectively. The overlapping ends may be fastened together by any suitable means, such as welding, riveting or bolting. The upper segments 21 of a ring are of materially greater thickness than its lower segments 28.

I claim:

1. A segmental, substantially circular tunnel lining wherein the segments forming the lower portion of the lining are materially of less strength than those forming the upper portion.

2. A tunnel lining comprising a plurality of rings placed substantially end to end, a plurality of segments forming the rings, the segments in the upper portion of the rings being of materially greaterstrength than the segments in the lower portion of the rings.

3. A tunnel lining comprising a plurality of metal segments, each segment comprising a shell bordered by flanges extending in circumferential and axial directions, said flanges projecting radially inward, and means for fastening the flanges of one segment to those of adjacent segments, the thickness of metal in the segments of the upper portion of the lining being materially greater than in the segments of the lower portion.

4. A tunnel lining comprising a plurality of rings placed co-axially end to end, a plurality of segments forming the rings, the segments being in the form of curved plates, the plates of a ring overlapping each other and those of adjacent rings, the plates in the upper portion of the rings being of materially greater thickness than those in the lower portion of the rings and means for fastening adjacent plates to each other.

5. A tunnel lining comprising a plurality of rings placed co-axially end to end, each ring comprisinga plurality of segments, the segments being in the form of plates curved circumferentially and corrugated axially, the plates of-a ring overlapping each other and those of adjacent rings, the plates in the upper portion of the rings being of materially greater strength than those in the lower portion of the rings and means for fasteningadjacent plates to each other.

ANDERS BULL. 

